Electrophotographic composition employing poly(vinyl-halobenzal)binder for organic photoconductors

ABSTRACT

DISCLOSED HEREIN ARE POLY(VINYL-HALOBENZAL) BINDERS FOR PHOTOCONDUCTOR COMPOSITIONS USED IN REPROGRAPHIC APPLICATIONS.

United States Patent Int. Cl. G03g 5/04 US. Cl. 961.5 9 Claims ABSTRACTOF THE DISCLOSURE Disclosed herein are poly(vinyl-halobenzal) bindersfor photoconductor compositions used in reprographic applications.

BACKGROUND OF THE INVENTION (1) 'Field of the invention This inventionrelates to binders for photoconductive compositions which are used inreprographic applications. More particularly, this invention relates topoly(vinylhalobenzal) binders for photoconductors which are used inelectrophotographic applications.

(2) Description of the prior art 'Electrophotography relates tosubstrates having a photoconductive substance coated thereon whichprovides a surface upon which images are reproducible. The substratemay, for example, be paper, glass, metal foil, transparent films such aspolyester film, cellulose acetate, nitrate, etc. The photoconductivesubstance is a material having electrical conductivity dependent uponthe amount of light to which it is subjected. Images to be reproducedare projected onto the charged, light sensitive surface which is exposedto illumination by conventional photographic methods whereby the coatinglocally dissipates its charge in proportion to the intensity ofillumination. Nonilluminated areas which retain their charge, are thentreated with electroscopic powder (e.g., colored synthetic resins)resulting in a visible image which may be transferred to another surfaceor may be fixed, e.g., by fusing, rendering the powder permanentlyadherent to the coating substrate. The rate at which the illuminatedcharged surface dissipates its charge is highly important to acommercially successful reproductive coating system. Higher dissipationrates usually result in faster reproduction processes. Conversely,systems with higher dissipation rates usually require less light in thereproduction process. Both of these factors directly aifect commercialacceptance of the system.

Fundamentally, electrophotographic systems comprise a photoconductor, abinder, which is usually an organic polymeric resin, for adhering thephotoconductor to the substrate to be coated and a dye sensitizer. Whilemuch success has been realized in the electrophotographic art, adefinite need still exists for new and improved binders which willprovide faster reproduction times in electrophotographic systems.Moreover, a need exists in the art for binders with improved stability,hardness, toughness and scratch resistance.

SUMMARY OF THE INVENTION The present invention fulfills theabove-mentioned need that exists in the art by providingpoly(vinyl-halobenzal) binders which allow fast reproduction processesin electrophotographic systems. Moreover, these binders exhibit improvedstability, hardness, toughness and scratch resistance which make themespecially suitable for use in transparencies and other relatedapplications where hardness in the binder is a desirable feature.

3,729,312 Patented Apr. 24, 1973 ice DESCRIPTION OF THE PREFERREDEMBODIMENTS The poly(vinyl-halobenzal) binders are prepared by heatingpolyvinyl alcohol and the appropriate halobenzaldehyde in a suitablesolvent in the presence of an acidic catalyst. The resulting'acetalization product is then neutralized, isolated, washed and dried,using standard procedures which are described in greater detail below.

The polyvinyl alcohol used to prepare the poly(vinylhalobenzal) ispartially or fully hydrolyzed material wherein the residual estercontent, calculated as polyvinyl acetate is in the range of from 0 to40% by weight and more preferably from 0 to 20% by weight. Polyvinylalcohols having a viscosity of from 1 to cps., when measured as a 4%aqueous solution viscosity at 20 C. are especially suited for thepreparation of the binders of the present invention.

The binders of the present invention have a hydroxyl content (measuredas polyvinyl alcohol) of from 6 to 20% by weight; a residual vinyl estercontent (calculated as polyvinyl acetate) of from O to 40% by weight;and a polyvinyl halobenzal content in the range of from 40 to 94% byweight. Preferably the binders of the present invention have a hydroxylcontent of from 8 to 12% by weight; a residual acetate content of from 0to 20% by weight; and a halobenzal content in the range of from 68 to92% by weight.

The preferred halogens for use in the present invention are chlorine andbromine with chlorine especially pre; ferred.

The amount of halogenation on the benzaldehyde starting material mayvary from mono to' penta substitution with the mono and disubstitutedhalogen derivatives being preferred.

Examples of the preferred binders would include:

poly (vinyl-2-chlorobenzal) poly (vinyl-3 -chlorobenzal) poly vinly-4-chlorobenzal poly(vinyl-3,4-dichlorobenzal),poly(vinyl-2,5-dichlorobenzal), poly (vinyl-3,6-dibromobenzal poly(vinyl-2,6-dichlorobenzal poly(vinyl-3,S-dichlorobenzal), poly(vinyl-2,3-dichlorobenzal) poly vinyl-2,4-dichlorobenzal poly(vinyl-2-bromobenzal) poly (vinyl-3-bromobenzal poly(vinyl-4-bromobenzal poly (vinyl-3,4-dibromobenzal),poly(vinyl-2,5-dibromobenzal poly (vinyl-2,6-dibromobenzal poly(vinyl-3,5-dibromobenzal), poly(vinyl-2,3-dibromobenzal),poly(vinyl-2,4-dibromobenzal) Especially preferred arepoly(vinyl-Z-chlorobenzal) and poly (vinyl-2,4-dichlorobenzal Thepoly(vinyl-halobenzal) binders of the present invention are used incombination with the well known photoconductors and dyes used inelectrophotographic reproducing processes.

Examples of the photoconductors used in the art include zinc oxide,titanium dioxide, etc., and organic photoconductors such as:

4,S-diphenyl-1,2-imidazolone; 4,S-diphenylirnidazole-Z-thione and theirderivatives; l-phenyl-3,5-bis(p-methoxy-styryl)pyrazoline; polymers ofN-vinyl carbazole; 4,4-dibromoterphenyl; poly(9-vinyl-anthraceneN,N,N',N-tetrabenzyl-p-phenylenediamine;

3 N,N,N',N'-tetra-o-chlorobenzyl-p-phenylenediamine;N,N,N,N'-tetra-(2,5-dimethylbenzyl)-p-phenylenediamine;N,N,N',N'-tetra-4-methylbenzyl-p-phenylenediamine;N,N,N',N-tetrabenzyloxydianiline;N,N'-diisopropyl-N,N-di(4-chlorobenzyl)-p-phenylenediamine;4-diethylamino-2-methyl-benzylideneazine;4-diallylamino-benzylideneazine; 4-diethylamino-benzylideneazine; N,N-di(2,5-dirnethylbenzyl) p-anisidine; 4-thiomethyl-N,N-dibenzylaniline; 4(4'-diethylaminobenzylidene -2-phenyl-5 (4) oxazoline;

etc.

These and other organic photoconductive Compounds are described indetail in US. Pats. 3,265,496; 3,447,922; 3,526,501 and 3,527,602, amongothers, and are incorporated herein by reference.

The dye sensitizers used in the electrophotographic reproducingprocesses are well known in the art and need no further descriptionhere. Examples of some of the dyes used are listed in US. Pat. 3,245,786which is incorporated herein by reference.

Electrophotographic coating compositions using thepoly(vinyl-halobenzal) binders of the present invention are prepared bydissolving the hinder, the photoconductor and any additional ingredientssuch as a dye in an appropriate solvent. Examples of such solvents wouldinclude halogenated hydrocarbons such as methylene chloride, methylenebromide, chloroform, bromoform, carbon tetrachloride, carbontetrabromide, ethylene dichloride, ethylene dibromide, ethylidenechloride, ethylidene bromide, s-tetrachloroethane, hexachloroethane,s-dichloroethylene, 1,1,l-trichloroethane, 1,1,2-trichloroethane,trichloroethylene, trimethylene bromide, trichlorobromoethane,trichloromethane, 1,2,3-trichloropropane, 1,1,2-trichloropropane,trifiuoro-1,2-tribromoethane, trifluoro-1,1, 2 trichloroethane, 2,2dichloro-l-bromoethane, 1,3-dichloro 2 methyl propane,1,2-dichloro-2-methyl-propane, 1,1-diiodoethane and the like.

Other solvents include N-methyl pyrrolidone, dialkyl formamides,dialkylacetamides and solvent blends of an aromatic hydrocarbon such asbenzene, toluene, xylene, etc., with aliphatic ketones, alcohols andesters. Specific examples of these solvent blends includetoluene-methanol; toluene-ethanol; toluene-methylethyl ketone,tolueneethyl acetate, toluene-ethanol-ethyl acetate; benzene-ethanolCellosolve acetate; xylene-ethanol; toluene-acetone, etc.

The ratio of binder to photoconductor in the electrophotographic coatingcompositions of the present invention will vary from (a) 1 part ofbinder to 10 parts of photoconductor to (b) 10 parts of binder to 1 partof photoconductor. The amount of dye used will vary from to 50,000 partsper million of photoconductor. The resin solids in the coatingcompositions will vary from 1 to 60% by weight based on the total weightof resin and solvent with from 3 to 50% by weight being preferred.

The coating compositions of the present invention are applied at coatingWeights of from 1 to 20 lbs. per 3000 sq. ft. of substrate and morepreferably at a coating weight of from 2 to lbs. per 3000 sq. ft. ofsubstrate. As is discussed in greater detail below, free films of thepoly(vinyl-halobenzal) binders of the present invention may be used asthe substrate. In this case they serve as a matrix for theorganophotoconductor, dye and any other ingredients. In thesesituations, the expression coating weight does ont really apply and thesystem is best described in the terms of film thickness of thepoly(vinylhalobenzal) based composition, which will be in the range offrom 1 to 50 mils and more preferably from 1 to mils.

The following examples are set forth in illustration of this inventionand should not be construed as a limitation thereof. Unless otherwiseindicated all parts and percentages given are by weight.

Examples 1 to 13 In these examples a poly(vinyl-2-chlorobenzal) resinhaving a polyvinyl alcohol content of 9.8% by weight and a residualacetate content in the range of from 0 to 2% by weight is used toillustrate the improved binders of the present invention.

The poly(vinyl-2-chlorobenzal) resin is prepared using the followingcharge:

Charge: Lbs.

Polyvinyl alcohol (1) 29.30 Ethanol 108.2 N-methyl pyrrolidone (NMP)108.2 2-chlorobenzaldehyde 51.2 Sulfuric acid 3.16

1 The polyvinyl alcohol has a residual acetate content in the range offrom O to 5% by weight and a viscosity in the range oi 2fon 4 to 6 cps.as measured as a 4% aqueous solution a 2 Commercially available fromTenneco.

The ingredients are slurried together and then the temperature is raisedto between and C. while maintaining agitation. As the reaction proceedsthe resulting poly(vinyl-2-chlorobenzal) resin goes into solution. Aftersix (6) hours the reaction mixture is neutralized with the followingcharge.

Neutralizing charge: Lbs. Potassium acetate 7.6

Water 5.26 N-methyl pyrrolidone 5.26

The resin solution is then disintegrated with water. The resulting resingrain is washed repeatedly with ethanol and water and dried at 45 C. for96 hours.

Electrophotographic coating compositions are prepared by dissolving 1.5grams of resin binder and 1.0 gram of a photoconductor in 13.5 grams ofchloroform. One milliliter (1 ml.) of a dye solution containing one gram(1 g.) of crystal violet in a liter of chloroform is then added to theresin binder-photoconductor solution.

The coating compositions are then applied to a commercially availableconductive base paper by means of a wire wound rod so as to obtain about4 dry lbs. of coating per 3000 sq. ft. After coating, the sheets aredried at 80- 100 C. for about one (1) minute to completely remove thesolvent. The coated stock is then conditioned overnight in the dark at70 F. and 50% relative humidity.

The photosensitivity of the coated stock is determined in a step wedgetest by placing a sheet of coated material, coated side up, on aOptographics Charging Easel (Optographics Corporation) charging thesurface negatively in the dark, using corona discharge; placing acalibrated 21 step sensitivity guide on the charged coated surface andsubjecting the assembly to 50 foot candles of light from a GB. 212enlarging bulb for 20 seconds. At the end of this period the sensitivityguide is removed and the image area treated with a positively chargedtoner powder to develop the remaining image. The photosensitivity of thecoating is defined as the highest step which produces a densityequivalent to the background density. The amount of exposure required toachieve this photosensitivity is then reported in terms offoot-candle-seconds (f.c.s.).

The results of these tests are tabulated in the following Table 1. Alsoincluded in Table 1 are the results of samples wherein polyvinylbutryral resin is used as the binder. The polyvinyl butyral resin ischaracterized as having a polyvinyl alcohol content in the range of from9 to 13% and a residual acetate content in the range of from 0 to 2.5%.Polyvinyl butyral resin has found widespread use as binder forphotoconductive compound and the examples using polyvinyl butyral as abinder are included as control examples to illustrate the suitability ofthe poly(vinyl-halobenzal) resins of the present invention as bindersfor photoconductive compounds.

TABLE 1.-SUMMARY OF STEP WEDGE TESTS FOR EX- AMPLES 1 TO 13 IN E.C.S.

Poly- (vinyl- Polychlorovinyl benzal) butyral Example Photoconductorbinder control 1 N11f,N,N'-tetrabenzyl-m-phenylene 49 309 am e. 2N,N,N,N'-tetra'chlorobenzyl-p- 123 1,000

phenylene diamlne. 3 N ,N-d.iisopropyl-N,N-di-p-chloro- 63 224benzyl-p-phenylene dial-nine. 4 N,N,N ,N-tetra(2,5-dimethyl benzyl- 162123 p-phenylene diamine. 5 N,N,N,N-tetrabenzyl-p-phenylene 89 123diamine. 6 N,N,N,N-tetra-p-methylbenzyi-p- 89 123 phenylene diamine. 7N,N,N',N-tetrabenzyl oxydianilino.. 89 224 8 4-dially1aminobenzilidenemine..." 12 123 4-diethylaminobenzilidene azine 224 604 104-dieithylamino-2-methy1benzilidene 17 49 az no. 114-thiomethyl-N,N-dibenzyl aniline 123 124-(4-diethylarninc-benzilidene-2- 64 123 phenyl-5(4) oxazolone. 13N,N-di(2,5-dimethylbenzyl)-p-anisidine 123 427 The data in Table 1illustrates that under comparable test conditions theelectrophotographic systems which use poly(vinyl-2-chlorobenzal) as thebinder component require considerably less energy to form an image thando the controls which use polyvinyl butyral as the binder component.This allows for faster electrophotographic processes under similar lightconditions. Conversely, the electrophotographic systems usingpoly(vinyl-2-chlorobenzal) as the binder component require less lightenergy in the electrophotographic processes than those systems usingpolyvinyl butyral as the binder.

Another aspect of the improved electrophotographic coatings which areprepared using a binder of the present invention is shown in the resultsof the standard Victoreen Test. Examples 1 to 13 above are subjected toa standard Victoreen Test and the results reported in Tables 2A and 213.

TABLE 2A.VIC1OREEN TEST RESULTS USING POLY- (VINYL 2-CHLOROBENZAL)BINDER TABLE 2B.VICTOREEN TESTS USING POLYVINYL BUTYRAL BINDER Satu-Dark Time Time ration decay to to )6 voltage rate volts voltage TheVictoreen instrument measures the charge capacity of a particularcoating, the ability of that coating to hold a charge in the dark andthe rate at which it loses or dissipates the charge under the influenceof specified light levels. The Victoreen tests are run under thefollowing conditions:

(a) Static test (b) 3 inches/second travel (c) Corona Current=35 micronamperes (d) Light=2 foot candles (f.c.)

The data in the Tables 2A and 2B show that the time to dissipate chargeto 50 volts for coatings using poly- (vinyl-2-chlorobenzal) as thebinder are consistently less than for those control compositions usingpolyvinyl butyral as the binder.

Still another facet of the present invention is illustrated by theMost-Stati Tester (M/ K Systems, Inc., Lynn, Massachuetts) whichillustrates the ability of the poly(vinylhalobenzal) based coatingcompositions to accept either positive or negative charges. In the Statitest, the paper is prepared as above using thepoly(vinyl-2-chlorobenzal) based coatings used in Examples 1 to 13 whichare then tested according to standard Stati Test procedures. The StatiTester results indicate that the poly(vinyl-halo- 3 2 benzal) basedcoating compositions of the present inven- Example voltage r v s voltagetron work equally well using either positive or neganve 0 7 264 0,34charges. This feature permits the coating compositions to 33 28 50 beused in wider, more varied applications. 255 1215 710 "7.0 The followingExamples 14 to 19 illustrate various 3? 28 21:2: electrophotoconductivecoating compositions using polygg 2; (vinyl halobenzal) resins of thepresent invention as 675 :5 10 11 2 binders. These resins are formulatedinto coatings using 23% f? gg: the photoconductor used in Example 1above, coated onto 55% 1.8 2.2 3. paper and tested as above. Results ofthese tests are tabu- 68 lated in the following Table 3.

TABLE 3.-SUMMARY 0F EXAMPLES 14 TO 19 Test Victoreen test Step wedgeSaturated Decay test, Ex. Binder Dye voltage rate Time 5 t.c.s.

14 Polyvinyl butyral (control) Violet 555 5.5 9.0 427 15 o..-

Cyanine. 475 2.5 30.0 912 16.-. Po1y(vinyl-2-chlorobenzal) "do-.- 3456.5 7.0 162 17--. Poly(vinyl-4-chlorobenzal) Violet. 280 2.0 36.0 60418--. Poly(vinyl-2,4-diehlorobenzal) do 400 2.0 2.2 309 19Poly(vinyl-3,4-d1cl1lorobenzal) Cyanine 295 11.0 30.0 912 1 Dark decayrate (initial voltage-voltage at end of 10 seconds in the dark, +10). 2Time to 50 volts, in seconds (measured from end of dark decay, under 20to. light).

Examples 14 to 19 illustrate some of the many variations that arepossible in electrophotoconductive coating compositions. The results ofthe Victoreen and step wedge tests further illustrate the variations inperformance that may be achieved by varying one of the components of thecoating compositions. Those skilled in the art are aware of thesevariations and select the components accordingly in order to tailor thecoating composition in order to meet the requirement of a givenapplication.

As stated above, certain applications require a degree of hardness inthe binder which is lacking in some of the binders of the prior art. Thehardness rating of a binder is conveniently measured on the binder infilm form using any one of several methods for determining hardness. Onesuch method is the pencil hardness test which is described by Gardnerand Sward at pages 131 and 132 of Paint Testing Manual, Physical andChemical Examination, Paints, Varnishes, Lacquers and Colors, 12thedition, March 1962, distributed by Gardner Laboratory, Inc., Bethesda,Maryland.

The pencil hardness test employs the following rating scale.

7B6B5B4B3B2BBHBH2H3H4H lillllllllll On this scale 7B has a very softrating while 7H has a very hard rating. Intermediate on the hardnessscale is a HB rating.

Pencil hardness tests are run on some binders of the present inventionand the results of this test are reported in the following Table 4.

TABLE 4.SUMMARY OF PENCIL The results of the foregoing table indicatethe superior hardness properties found in the poly(vinyl-halobenzal)binders of the present invention.

Electrophotographic conductive coatings based on thepoly(vinyl-halobenzal binders of the present invention may be coatedonto a variety of substrates in order to obtain reprographic articles.These substrates include paper, glass, metal foils and transparentfilms. Examples of the transparent films include polyester film such'aspolyethylene terephthalate, cellulose acetate, cellulose nitrate,cellulose butyrate, cellophane, etc.

The poly(vinyl-halobenzal binders of the present invention have goodfilm forming properties and dried films exhibit good toughness,hardness, clarity, etc. This enables these binders to be cast into filmswhich may be used in place of the transparent films referred to above inthe manufacture of reprographic transparencies. When used in thismanner, they may be considered as being a substrate as well as thematrix binder in which the organic photoconductor, dye or any otheradditive is dispersed. This provides a decided advantage in themanufacture of reprographic films and transparencies.

From the foregoing it should be apparent that many variations may bemade in the present invention without departing from the spirit andscope thereof.

What is claimed is:

1. In an electrophotographic composition comprising a photoconductor, adye sensitizer and a resinous binder wherein the weight ratio of binderto photoconductor is in the range of 1:10 to 10:1 and wherein there areup to 50,000 parts by weight of dye sensitizer per million parts byweight of photoconductor, the improvement which comprises using apoly(vinyl-halobenzal) as the resinous binder.

2. The improved electrophotographic composition of claim 1 wherein theresinous binder is a poly(-vinyl-ch1orobenzal).

3. The improved electrophotographic composition of claim 2 wherein theresinous binder is poly(vinyl-2,4-dichlorobenzal) 4. The improvedelectrophotographic composition of claim 2 wherein the resinous binderis poly(vinyl-2,4- dichlorobenzal.

5. The improved electrophotographie composition of claim 2 wherein theresinous binder is poly(vinyl-3,4- dichlorobenzal) 6. In anelectrophotographic composition comprising a photoconductor, a dyesensitizer and a resinous binder wherein the weight ratio of binder tophotoconductor is in the range of 1:10 to 10:1 and wherein there are upto 50,000 parts by weight of dye sensitizer per million parts by weightof photoconductor, the improvement which comprises using as the resinousbinder, a poly (vinyl-chlorobenzal) having a hydroxyl content of from 6to 20% by weight, and a residual vinyl ester content of from 0 to 40% byweight.

7. The improved electrophotographic composition of claim 6 wherein theresinous binder is a poly(vinyl-2-chlorobenzal).

8. The improved electrophotographic composition of claim 6' wherein theresinous binder is poly(vinyl-2,4-dichlorobenzal) 9. The improvedelectrophotographic composition of claim 6 wherein the resinous binderis poly(vinyl-3,4-dichlorobenzal) References Cited UNITED STATES PATENTS3,437,481 4/1969 Graver et a1. 96l.8 3,554,746 1/1971 Merrill 96-15 XOTHER REFERENCES Chemical Abstracts: vol. 67, 1967, 22,335y; vol. 68,1968, 50,4241; vol. 68, 1968, 79,443g.

GEORGE F. LESMES, Primary Examiner J. R. MILLER, Assistant Examiner US.Cl. X.-R. 961.8; 260--73

